Heat-sensitive recording paper

ABSTRACT

The present invention provides a novel bis(phenoxymethyl)benzene derivative or bis(naphthoxymethyl)benzene derivative, which improves the stability of image on a heat sensitive recording paper composed of a leuco dye and a developer.

This application is a division, of application Ser. No. 066,476, filedJune 26, 1987 U.S. Pat. No. 4,855,482.

BACKGROUND OF THE INVENTION

The present invention relates to bis(phenoxymethyl- andnaphthoxymethyl)benzene derivatives which have been newly developed andtheir application to a heat sensitive recording paper.

In general, a heat sensitive recording paper in wide use is of the typein which a paper substrate is provided thereon with a colorant which isa colorless or pale-colored dye referred to as a leuco dye hereinafter,a phenolic compound which, as a developer, makes such a colorant assumea color when heated, a binder, a filler, an excipient, a lubricant, andother auxiliaries.

A heat sensitive recording paper produces an image in color by aninstantaneous chemical reaction between a colorant and a developer whenheat is applied thereto, and the applicability has been expanded fromthe use for copying of documents and printed matter into thermal pentype recorders in instrumentation, thermal printers, heat sensitive typeautomatic ticket vending machines, facsimile, etc. Especially where theapplication is in the information-related areas such as facsimile,demand is high for speedier operation of the apparatuses and therefore,heat sensitive recording paper used therein is required to have anability to produce recording images of high densities speedily.

In the application of a phenolic compound as a developer,p-hydroxybenzoic acid esters, especially benzyl p-hydroxybenzoate, areknown to be suitable for high speed heat sensitive recording (reference:Japanese Patent Publication Toku Kai Nos. Sho 52-140483, 56-144193,57-82089 and 57-107885). A heat sensitive recording paper containing oneof such developers lends itself to speeding up heat sensitive recording,showing a good coloring effect, producing brilliant recording images ofhigh densities, and the plain surface being impaired much less by fog.However, the recording images developed are lacking in stability, fadingand white spotting of the developed images being known as the defects.Although the reason for these defects may not always be clear, thisinstability is identified as crystallization of the p-hydroxybenzoicacid ester by loosening itself from the charge-transfer complex of thecolorant and the p-hydroxybenzoate. It has been attempted to preventthis crystallization by addition of a certain compound but the result isnot quite satisfactory.

With the above-mentioned defects taken into account the presentinventors, in their research on heat sensitive recording paper,discovered new compounds which prevent the fading and the white spottingand brought the research to this invention.

SUMMARY OF THE INVENTION

The present invention provides a novel compound represented by aformula: ##STR1## wherein: A represents a group ##STR2## where Rrepresents a C₁ -C₄ alkyl group, phenyl group or benzyl group, and Xrepresents hydrogen atom or halogen atom.

The compounds improve the stability of image on a heat sensitiverecording paper composed of a leuco dye and a developer, especiallyphenolic hydroxyl group-containing acid esters.

DETAILED DESCRIPTION OF THE INVENTION

The first object of the present invention is to provide abis(phenoxymethyl)benzene derivative or bis(naphthoxymethyl)benzenederivative, expressed by a general formula: ##STR3## wherein: Arepresents a group ##STR4## where R represents a C₁ -C₄ alkyl group,phenyl group or benzyl group and X represents hydrogen atom or halogenatom.

The second object of the present invention is to provide a color formingcomposition for a heat sensitive recording paper, which contains theabove compounds represented by the formula I, leuco dye and phenoliccompound as an essential material on a sheet.

The third object of the present invention is to provide a heat sensitiverecording paper which contains in its heat sensitive layer a leuco dye,developer, and one of the compounds expressed by a general formula I.

The compound expressed by the formula I can be produced, for example, bydehydrohalogenation between an alkaline salt of an aromatichydroxycarboxylic acid ester which is expressed by a general formula:

    A--OH                                                      II

wherein: A is the same as in Formula I, and xylylene dihalogenoid whichis expressed by a general formula ##STR5## wherein Y represents ahalogen atom.

The alkaline salt of the compound expressed by the formula II may be,for example, a sodium salt or a potassium salt.

It is preferable to have this reaction take place in the presence of asolvent. The solvent suitable for this purpose is a polar aproticsolvent, such as N,N-dimethylformamide, N,N-dimethylacetamide ordimethyl sulfoxide. The reaction takes place for 1-8 hours attemperatures 50°-150° C.

After the reaction water is added to the reaction liquid and theprecipitate is filtered out from the liquid and recrystallized into arefined compound expressed by said formula I.

The compounds expressed by said formula I include:

1,2-, 1,3- or 1,4-bis(o-carboalkoxy-phenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(m-carboalkoxy-phenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(p-carboalkoxy-phenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(2-carboalkoxy-1-naphthoxymethyl) benzene,

1,2-, 1,3- or 1,4-bis(4-carboalkoxy-1-naphthoxymethyl) benzene,

1,2-, 1,3- or 1,4-bis(1-carboalkoxy-2-naphthoxymethyl) benzene,

1,2-, 1,3- or 1,4-bis(3-carboalkoxy-2-naphthoxymethyl) benzene, and

1,2-, 1,3- or 1,4-bis(6-carboalkoxy-2-naphthoxymethyl)benzene,

and a compound such as one of the above which contains a carbophenoxygroup or a carbobenzyloxy group instead of a carboalkoxy group.

Further, the compounds of the present invention include any compounds ofwhich phenoxy or naphthoxy group has halogen substituents such aschloro-, bromo-, fluoro- and iodo-substituent. The position of thesubstituent is not restricted. Examples of the compound of which phenoxyor naphthoxy group is substituted with halogen are:

1,2-, 1,3- or 1,4-bis(2-halogeno-4-carbobenzyloxyphenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(3-halogeno-4-carbobenzyloxyphenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(3-halogeno-2-carbobenzyloxyphenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(4-halogeno-2-carbobenzyloxyphenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(2-halogeno-4-carboalkoxyphenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(3-halogeno-4-carboalkoxyphenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(4-halogeno-2-carboalkoxyphenoxymethyl)benzene,

1,2-, 1,3- or 1,4-bis(2-halogeno-3-carboalkoxyphenoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(2-halogeno-4-carboalkoxy-1-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(4-halogeno-2-carboalkoxy-1-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(6-halogeno-2-carboalkoxy-1-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(8-halogeno-4-carboalkoxy-1-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(8-halogeno-6-carboalkoxy-1-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(1-halogeno-4-carboalkoxy-2-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(4-halogeno-1-carboalkoxy-2-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(6-halogeno-8-carboalkoxy-2-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(8-halogeno-6-carboalkoxy-2-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(4-halogeno-6-carboalkoxy-2-naphthoxymethyl)benzene,

1,2-, 1,3- or1,4-bis(1-halogeno-8-carboalkoxy-2-naphthoxymethyl)benzene, and thelike.

The carboalkoxy group in a compound expressed by the formula I may be,for example, carbomethoxy group, carboethoxy group, carbopropoxy group,or carbobutoxy group.

In producing a heat sensitive recording paper according to the presentinvention, a leuco dye, a developer, and a compound expressed by theformula I are compounded: for 100 parts by weight of a leuco dye100-1000 parts by weight of a developer is preferably employed, and for100 parts by weight of a developer a compound expressed by the formula Iis preferably employed in a proportion in the range 1-200, especially3-100 parts by weight.

The leuco dyes applicable to the practice of this invention, forexample, include those of the types of triphenylmethane, fluoran,phenothiazine, auramine, and spiropyran. These dyes are employed eachsingly or in a mixture of two dyes or more. Some examples of these leucodyes are as follows:

3,3-bis(p-dimethylaminophenyl)phthalide,

3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide,

(called also crystal violet lactone),

3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide,

3,3-bis(p-dimethylaminophenyl)-6-chlorphthalide,

3,3-bis(p-dibutylaminophenyl)phthalide,

3-cyclohexylamino-6-chlorfluoran,

3-dimethylamino-5,7-dimethylfluoran,

3-diethylamino-7-chlorofluoran,

3-diethylamino-7-methylfluoran,

3-diethylamino-7,8-benzfluoran,

3-diethylamino-6-methyl-7-chlorfluoran,

3-(N-p-tolyl-N-ethylamino)-6-methyl-7-anilinofluoran,

3-pyrrolidino-6-methyl-7-anilinofluoran,

2-N-(3'-trifluormethylphenyl)amino-6-diethylaminofluoran,

2-3,6-bis(diethylamino)-9-(o-chloranilino)xanthylium benzoic acidlactam,

3-diethylamino-6-methyl-7-(m-trichloromethylanilino)fluoran,

3-diethylamino-7-(o-chloranilino)fluoran,

3-dibutylamino-7-(o-chloranilino)fluoran,

3-N-methyl-N-amylamino-6-methyl-7-anilinofluoran,

3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluoran,

3-diethylamino-6-methyl-7-anilinofluoran,

3-(N,N-diethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran, benzoylleucomethylene blue,

6'-chloro-8'-methoxy-benzoindolyno-pyrylospiran,

6'-bromo-3'-methoxy-benzoindolyno-pyrylospiran,

3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlor-phenyl)phthalide,

3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-nitro-phenyl)phthalide,

3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methyl-phenyl)phthalide,

3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chlor-5'-methylphenyl)phthalide,

3-morpholino-7-(N-propyl-trifluoromethylanilino)fluoran,

3-pyrrolidino-7-trifluoromethylanilinofluoran,

3-diethylamino-5-chloro-7-(N-benzyl-trifluoromethylanilino)fluoran,

3-pyrrolidino-7-(di-p-chlorphenyl)methylaminofluoran,

3-diethylamino-5-chlor-7-(α-phenylethylamino)fluoran,

3-(N-ethyl-p-toluidino)-7-(α-phenylethylamino)fluoran,

3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran,

3-diethylamino-5-methyl-7-(α-phenylethylamino)fluoran,

3-diethylamino-7-piperidinofluoran,

2-chloro-3-(N-methyltoluidino)-7-(p-n-butylanilino)fluoran,

3-(N-benzyl-N-cyclohexylamino)-5,6-benzo-7-α-naphthylamino-4'-bromofluoran,and

3-diethylamino-6-methyl-7-mesitydino-4',5'-benzofluoran.

The developers used in the heat sensitive printing paper may be phenolichydroxyl group containing compounds which have been used in aconventional heat sensitive printing paper. Preferable phenoliccompounds are esters of mono- or polyphenols having a hydroxyl group andcarboxyl group such as hydroxybenzoic acid esters, alkyl gallate, tannicacid esters and the like. The most preferable one is p-hydroxybenzoatesuch as methyl p-hydroxybenzoate, ethyl-, propyl-, isopropyl-, butyl-,isobutyl-, hexyl-, benzyl-, phenetyl-, phenyl-, or naphthylp-hydroxybenzoate.

In order to prepare the color forming composition for the heat sensitiveprinting paper according to the present invention the compoundrepresented by the formula I, the developer and leuco dye may be mixedunder the condition that the melted compound and developer are notcontacted with the leuco dye. The color forming composition may be adispersion type, solution type and hot-melt type, but the solution typeand the hot melt type must be separated in order to prevent colordeveloping before use. Most preferable color forming compositioncomposition is a dispersion type, especially dispersion-in-water type.

In order to prepare the dispersion type composition the compoundrepresented by the formula I alone or with the developer is dispersed ina suitable medium such as water, and mixed with dye which is alsodispersed in a medium such as water. The compound represented by theformula I and developer may be separately dispersed or the both may behomogenously mixed, fused and powdered before the dispersion.

At the dispersion these materials are ground into fine particles in amedium, especially water by means of a grinder, such as a ball mill,Atrighter or sand-grinder, or by means of a suitable emulsifying meansand prepared, together with additives, into liquid coatings.

The additives used to make the color forming composition are, forexample, a binder, for which are used polyvinyl alcohol, hydroxyethylcellulose, methyl cellulose, starch, styrene-maleic anhydride copolymer,vinylacetate-maleic anhydride copolymer, styrene-butadiene copolymer,etc., a filler, for which are used kaolin, diatomaceous earth, talc,titanium oxide, calcium carbonate, magnesium carbonate, aluminumhydroxide, etc., an excipient, for which are used fatty acid metallicsalts such as zinc stearate, aluminum stearate, calcium stearate, zincoleate, etc., a lubricating agent, for which are used waxes such asparaffin wax, carnauba wax, polyethylene wax, etc., a UV ray absorbent,for which benzophenones and triazoles are used, a waterproofing agentsuch as glyoxal, a dispersion liquid, a defoaming agent, etc.

A heat sensitive recording paper provided by the present invention isobtained by coating a substrate, such as paper or film, with a colorforming composition prepared as above with use of additives. If desired,a heat sensitive recording paper having two layer, e.g. leuco dye layerand developer layer with the compound represented the formula I on papermay be prepared.

A heat sensitive recording paper thus obtained according to the presentinvention exhibits advantages in good coloring effect, adaptability tohigh speed recording, and stability of the coating, and the imagesproduced thereon show an excellent stability with improvement in theliability to fading and white spotting.

EXAMPLE 1 Synthesis of 1,3-bis(p-carbobenzyloxyphenoxymethyl)-benzene

To a solution of p-hydroxybenzoic acid benzyl ester (45.6 g, 0.2 mol) in200 ml N,N-dimethylformamide, sodium carbonate (10.6 g, 0.1 mol) wasadded and stirred for 10 minutes at room temperature. Then a solution ofm-xylylenedichloride (17.3 g, 0.1 mol) in 100 ml ofN,N-dimethylformamide was added in drops to the reaction mixture in 10minutes. The reaction mixture stirred at 113° C. for 4 hours, cooled andblown into water, and the obtained precipitate was filtered, rinsed withwater. Then crued product was suspended in methanol and stirred at 60°C. for 30 minutes, cooled, filtered, and gave 15.8 g (yield 26.9%) of1,3-bis(p-carbobenzyloxyphenoxymethyl)-benzene: m.p. 92.5°-93.8° C.

NMR value: δ 5.11 (4H, s), 5.33 (4H, s), 6.91-8.07 (22H, m).

Mass value: m/z=558 (M⁺).

    ______________________________________                                        Element analysis values                                                                     C        H     O                                                ______________________________________                                        Calculated value (%)                                                                          77.4       5.4   17.2                                         Measured value (%)                                                                            76.8       5.5   17.7                                         ______________________________________                                    

EXAMPLE 2 Synthesis of 1,4-bis(p-carbobenzyloxyphenoxymethyl)benzene

To a solution of p-hydroxybenzoic acid benzyl ester (68.4 g, 0.3 mol) inN,N-dimethylformamide (274 g) sodium carbonate (15.9 g, 0.15 mol) wasadded, and stirred at 100° C. Then, p-xylylenedichloride (26.2 g, 0.15mol) was added to the reaction mixture in 10 minutes, and stirred at100° C. for one hour. Water was added to the resultant to separate aclued precipitate. The precipitate was filtered, added toN,N-dimethylformamide to be dissolved at 90° C., cooled, filtered, anddried to give a white crystal of1,4-bis(p-carbobenzyloxyphenoxymethyl)benzene (27.8 g, yield 33.0): m.p.154°-157° C.

NMR values: δ 5.11 (4H, s), 5.33 (4H, s), 6.92-8.07 (22H, m).

Mass value: m/z=558 (M⁺).

    ______________________________________                                        Element analysis values                                                                     C        H     O                                                ______________________________________                                        Calculated value (%)                                                                          77.4       5.4   17.2                                         Measured value (%)                                                                            76.8       5.5   17.7                                         ______________________________________                                    

EXAMPLE 3 Synthesis of 1,3-bis(6-carbomethoxy-2-naphthoxymethyl)benzene

To sodium salt of 2-hydroxynaphthalene-6-carboxylic acid methyl ester(44.8 g) N,N-dimethylformamide (200 ml) was added with stirring at roomtemperature. Then a solution of m-xylylenedichloride (17.5 g, 0.1 mol)in N,N-dimethylformamide was added in drops thereto in 10 minutes. Thereaction mixture was stirred at 105° C. for 4 hours and then cooled togive a precipitate. The precipitate was rinsed withN,N-dimethylformamide, treated with hot water at 80° C. for 30 minuteswith stirring, and then with methanol at 60° C. for 30 minutes withstirring; cooled, filtered and dried to give a white crystals of1,3-bis(6-carbomethoxy-2-naphthoxymethyl)benzene (39.7 g, yield 77.8%):m.p. 177.3°-178.0° C.

NMR values: δ 3.95 (6H, s), 5.21 (4H, s), 7.20-8.52 (16H, m).

Mass value: m/z=506 (M⁺)

    ______________________________________                                        Element analysis values                                                                     C        H     O                                                ______________________________________                                        Calculated value (%)                                                                          75.8       5.1   19.1                                         Measured value (%)                                                                            75.7       5.2   19.1                                         ______________________________________                                    

EXAMPLE 4 Synthesis of 1,3-bis(m-carbomethoxyphenoxymethyl)benzene

To a solution of m-hydroxybenzoic acid methyl ester (30.4 g, 0.2 mol) in150 ml methanol sodium methylate (38.6 g, 0.2 mol) was added. Themixture was stirred at 100° C. for one hour, cooled and dried. To thedried product N,N-dimethylformamide (150 ml) was added and thenm-xylylenedichloride (17.5 g, 0.1 mol); and stirred at 110° C. for 2hours. After cooled, the precipitate was filtered off, and the obtainedfiltrate was blown into water-methanol (1:1) and then filtered. Theprecipitate obtained was treated with methanol, and dried to give awhite crystale of 1,3-bis(m-carbomethoxy-phenoxymethyl)benzene (28.3 g,yield 69.7%): m.p. 57.8-58.5.

EXAMPLE 5 Synthesis of 1,4-bis(o-carbomethoxyphenoxymethyl)benzene

To a solution of salicylic acid methyl ester (45.6 g, 0.3 mol) in 150 mlN,N-dimethylformamide sodium carbonate (18.0 g, 0.17 mol) was added,stirred at 100° C., and then p-xylylenedichloride (29.8 g, 0.17 mol) wasadded thereto. The mixture was reacted at 144° C. for 8 hours. After thereaction, the obtained mixture was cooled and blown into water to give aprecipitate, which was then filtered. The filtered precipitate wastreated with hot methanol and dried to give a white crystal of1,4-bis(o-carbomethoxyphenoxymethyl)benzene (8.3 g, yield 14%): m.p.115°-120° C.

EXAMPLE 6 Synthesis of1,3-bis(2-chloro-4-carbobenzyloxyphenoxymethyl)-benzene

To a solution of 2-chloro-4-hydroxybenzoic acid benzyl ester (26.3 g,0.1 mol) in 100 ml N,N-dimethylformamide sodium carbonate (5.3 g, 0.05mol) was added, and stirred for 10 minutes at room temperature. Then asolution m-xylylenedichloride (8.8 g, 0.05 mol) in 50 mlN,N-dimethylformamide was added in drops to the reaction mixture in 10minutes. The reaction mixture is stirred at 120° C. for 2 hours, cooledand blown into water to give a precipitate. The obtained precipitate wasfiltered, and rinsed with water. Then crued product was suspended inmethanol and stirred at 60° C. for 30 minutes, cooled and filtered, andgave a white drystal of1,3-bis(2-chloro-4-carbobenzyloxy-phenoxymethyl)-benzene (25.2 g, yield80%): m.p. 95.8°-97.0° C.

EXAMPLE 7

    ______________________________________                                        Liquid A (dye-dispersed liquid)                                               3-(N--cyclohexyl-N--methylamino)-6-methyl-                                                               4.0 parts                                          7-anilinofluoran                                                              10% polyvinyl alcohol water solution                                                                     9.2 parts                                          water                      5.0 parts                                          Liquid B (developer-dispersed liquid)                                         p-hydroxybenzoic acid benzyl ester                                                                       6.0 parts                                          1,3-bis(p-carbobenzyloxy-phenoxymethyl)                                                                  0.6 parts                                          benzene                                                                       10% polyvinyl alcohol water solution                                                                     30.0 parts                                         ______________________________________                                    

The Liquids A and B were ground in a ball mill respectively, and 1.0parts by weight of the Liquid A and 4.0 parts by weight of the Liquid Bwere mixed to prepare a color forming composition. The color formingcomposition was applied to a base paper by means of a wire bar to give aheat sensitive recording paper (coating 6 g/m²).

EXAMPLE 8

A heat sensitive recording paper was obtained in the same manner as inthe example 7, except that1,4-bis(p-carbobenzyloxy-phenoxymethyl)benzene was used instead of1,3-bis(p-carbobenzyloxy-phenoxymethyl)benzene.

EXAMPLE 9

A heat sensitive recording paper was obtained in the same manner as inthe example 7, except that1,3-bis(6-carbomethoxy-2-naphthoxymethyl)benzene was used instead of1,3-bis(p-carbobenzyloxy-phenoxymethyl)benzene.

EXAMPLE 10

A heat sensitive reporting paper was obtained in the same manner as inthe Example 7, except that1,3-bis(2-chloro-4-carbobezyloxy-phenoxymethyl)benzene was used insteadof 1,3-bis(p-carbobenzyloxy-phenoxymethyl) benzene.

REFERENCE EXAMPLE

A heat sensitive recording paper was obtained in the same manner as inthe Example 7, except that1,3-bis(p-carbobenzyloxy-phenxoymethyl)benzene was not used.

[EXPERIMENT 1]

Five kinds of heat sensitive recording paper, obtained in the examples7-10 and in the Reference Example, were tested with respect to the plainsurface and image density, first with the image developed at 120° C. andsecondly when the heat sensitive recording paper was held for 24 hoursunder the conditions of (1) 40° C. and 90% humidity, and (2) 60° C. Theresults are shown in Table 1. A heat sensitive recording paper of thepresent invention apparently showed a less variation in image densitywith time, and was excellent in a keeping stability in comparison withthe heat sensitive recording paper in the Reference Example.

                                      TABLE 1                                     __________________________________________________________________________                                             Plain surface                                     Image preservation stability     After                                        After 24 hours                   24 hours'                              Image standing at 40° C.                                                                   After 24 hours'    standing                                                                           After                             density                                                                             and 90% humidity                                                                            standing at 60° C.                                                                   Density                                                                            at 40° C.                                                                   24 hours'                         when  Preservation  Preservation  before                                                                             and 90%                                                                            standing                          developed                                                                           rate (%)                                                                             Appearance                                                                           rate (%)                                                                             Apperance                                                                            test humidity                                                                           at 60° C.           __________________________________________________________________________    Example 7                                                                            1.07  100     O     118     O     0.13 0.13 0.14                       Example 8                                                                            0.94  93     O      98     O      0.12 0.14 0.14                       Example 9                                                                            1.01  88     O      126    O      0.12 0.13 0.14                       Example 10                                                                           1.04  106    O      107    O      0.11 0.13 0.13                       Comparison                                                                           1.26  83     Δ                                                                              84     Δ                                                                              0.13 0.13 0.15                       __________________________________________________________________________     O No or virtually no change                                                   X Fades in mottles                                                            Δ A few fades in mottles                                           

[EXPERIMENT 2]

Two kinds of heat sensitive recording paper, obtained in the Example 7and the Reference Example, were tested with respect to change of imagedensity. They were subjected to a rigid condition of 60° C. and 90%humidity, under which they were held for 24 hours after development at120° C. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                  Image preservation stability                                                  Preservation rate (%)                                                                         Appearance                                          ______________________________________                                        Example 7   101                O                                              Reference Example                                                                          74               X                                               ______________________________________                                          O: No or virtually no change                                                  X: Fades in mottles or white crystals separate out.                     

What is claimed is:
 1. A heat sensitive recording paper which containsin its heat sensitive layer a leuco dye, developer, and either of abis(phenoxymethyl)benzene derivative or bis(naphthoxymethyl)benzenederivative having the general formula (I): ##STR6## wherein: Arepresents a group ##STR7## where R represents a C₁ -C₄ alkyl group, aphenyl group or benzyl group, and X represents hydrogen atom or halogenatom.
 2. The heat sensitive recording paper of claim 1, wherein saiddeveloper is a phenolic hydroxyl group containing compound.
 3. The heatsensitive recording paper of claim 1, wherein said developer is ahydroxybenzoic acid ester.
 4. The heat sensitive recording paper ofclaim 1, wherein said leuco dye, developer and bis (phenoxymethyl)benzene derivative or bis (naphthoxymethyl) benzene derivative expressedby the formula (I) is dispersed in a liquid medium.
 5. The heatsensitive recording paper of claim 4, wherein said liquid medium iswater.
 6. The heat sensitive recording paper of claim 1, wherein saiddeveloper is contained in a range of 100-1000 parts by weight based on100 parts by weight of said leuco dye, and said compound represented bythe formula (I) is in 1-200 parts by weight based on 100 parts by weightof said developer.
 7. The heat-sensitive recording paper of claim 1,wherein said bis(naphthoxymethyl)benzene derivative is a 1,3 benzenederivative, wherein A is naphthylene, R is benzyl and X is hydrogen. 8.The heat-sensitive recording paper of claim 1, wherein said benzenederivative is a 1,2 benzene derivative, wherein A is naphthylene, R isbenzyl an X is hydrogen.
 9. The heat-sensitive recording paper of claim1, wherein said benzene derivative is a 1,2 benzene derivative wherein Ais naphthylene, R is C₁ alkyl and X is hydrogen.
 10. The heat-sensitiverecording paper of claim 1, wherein said benzene derivative is a 1,4benzene derivative, wherein A is naphthylene, R is benzyl and X ishydrogen.